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Thread: Fast Fred's Secrets of the OMC MOD50's Thread #1

  1. #21
    BoatRacingFacts VIP
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    Quote Originally Posted by David_L6
    I wonder what those motors were turning with a racing lower unit on a tunnel hull and how many horsepower they were making at those RPM's???
    Quote Originally Posted by Fast Fred
    hp falls off, but that don't mean she won't keep turnin up, which will give the hull some vary long legs.

    Anyone have any idea what kind of RPM's they were getting out of those motors on tunnel hulls?

    Fred, what if the compression was bumped up a bit? (McDaniels piston on left, factory piston on right.)
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    David



    FOR SALE: FE / SE / 850 Mod motor parts
    http://www.boatracingfacts.com/forum...od-motor-parts

  2. #22
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    more compression would make more hp, but not nessasarly more rpms,

  3. #23
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    higher ports make more rpms, a lot of other factor come in to play, I think it'll
    pull in to the 8's, after that, ???, i'll have to let ya Know

  4. #24
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    Thumbs up

    thanks for that the shot of them bullets thare DavidL6

  5. #25
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    Quote Originally Posted by Fast Fred
    thanks for that the shot of them bullets thare DavidL6
    No problem..... Can take as many as you want and e-mail them to you.
    David



    FOR SALE: FE / SE / 850 Mod motor parts
    http://www.boatracingfacts.com/forum...od-motor-parts

  6. #26
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    see if this works, got a chart of a small 2 stroke, this one is vary pumped up,
    see how it responds ,

  7. #27
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    same moda stock,

  8. #28
    Sam Cullis Mark75H's Avatar
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    There is something weird about the way those graphs are set up .... they are not presented in the same format ... they are not a direct comparison .... closer than apples and oranges, but as different as Granny Smiths and Red Delicous apples. Each graph is correct to itself, but the 2 graphs are not comparisons
    Last edited by Mark75H; 01-01-2006 at 10:15 AM.
    Since 1925, about 150 different racing outboards have been made.


  9. #29
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    ???, I don't know, this is what i think i know about the two, maybe that helps.
    same motor, 52cc, stock clutch comes in at 2 grand makes a pull, peaks at
    3.4-3.5hp @ about 7500.

    same motor , new carb same size +1/2, biger intake, port the bag out of the jug, w/ exspando pipe,
    plug in make a pull, clutch comes in at 2grand, (i'm thinkin the pull is the same, the drag, the load,???) pulled to 9 donkeys @ like 9600
    was just lookin at it for how the power curve looks as she runs on past peak
    Last edited by Fast Fred; 01-01-2006 at 12:10 PM.

  10. #30
    Sam Cullis Mark75H's Avatar
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    Correct. Each graph is correct to itself, but on the second both the hp and torque lines go 1-2-3-4 ... on the first one the hp goes 2-4-6-10 and the torque still goes 1-2-3-4

    There is no information about the clutch action ... all the graph shows is that we know nothing about the power below 2,000 rpm. Either readings were not taken or the person presenting the data chose not to tell us, we do not know.

    Stock made 1.1 hp @2k and mod was sacrificed to about .89 hp @2k
    stock pulled 2.5 @4k, mod still slouched with 1.9@4k
    stock pulled 2.8 @5k, mod broke even @5k with 2.8hp

    Since chart 2 uses 1:1 ratio between hp and torque representations we see hp and torque at the same point on the graph at 5,250 rpm ... 2.96 or so. (The the stock motor's torque passed its peak at 4k and is falling gently, so with rpm increasing hp is also still increasing.)

    Chart 1 shows that torque and hp are about 2.99 at 5,250 rpm on the mod motor, but since the scales are different they don't fall on the same point and the lines do not cross. The mod motor has not yet reached its torque peak, as rpm increases hp is increasing dramatically compared to the stock motor.

    At 7,500 rpm the stock motor is maxed out at something like 3.6hp - the mod motor has almost TWICE the power, about 6.5hp, and has still not reached its torque peak nor hp peak. Hp is still increasing dramatically with rpm.

    At 8,500 the mod motor's torque peaks at about 5.3, but with a smooth top to the torque curve, power is maybe 8.8 and still increasing with rpm increase. 30% more torque at double the rpm ... getting power from both hp factors.

    At 9,600 the mod motor peaks out over 9hp. Hp no longer increases with further rpm increase because torque is falling dramatically with rpm increase; but hp stays over 5 hp past 11,000 where the stock motor was stuck at 3.5.

    With a sliding length expansion chamber the torque may have risen even sooner ... the torque bump that starts at 7,000 could have started at 5,000 rpm. With a little luck the hp at 6,000 rpm would be increased from 4hp to 6hp and the torque drop at 9,600 could have been pushed to 11,000 and the hp bumped from 9 to 11 due to the rpm increase.
    Last edited by Mark75H; 01-02-2006 at 09:07 PM.
    Since 1925, about 150 different racing outboards have been made.


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